Device comprising a shaft and at least one hub which is attached to said shaft, and a method for producing this device

ABSTRACT

The device comprises a shaft ( 1 ) and a hub ( 2 ) which is attached to said shaft. One of the edges ( 10 ) of the opening ( 5 ) in the hub ( 2 ) through which the shaft ( 1 ) should be passed has a curved profile ( 11 ). This profile ( 11 ) of the hub edge ( 10 ) is tangentially connected to the inner surface ( 6 ) of the hub opening ( 5 ).

The present invention relates to a device with a shaft and with at leastone hub attached to this shaft and to a method for manufacturing of thisdevice.

A device of this type is disclosed e.g. in EU-PS 0 521 354. The shaft ofthis device shows the usual overmeasure with respect to the opening ofthe hub. The wall opening in the hub has the shape of a cylinder. Thatone side of the opening in the hub from which the shaft is to be ledinto the hub is widened, having the shape of a funnel. Otherwiseexplained, this means that the margin of the opening in the hub isprovided with a phase. The inclined wall of this phase has the shape ofa cone. If a vertical section is carried out in such a manner that themain axis of the opening is placed in the section plane, then the cutacross the phase appears as a straight line. Between said straight lineand the equally straight running surface line of the cylindrical openingof the hub, a blunt angle is present.

Said phase facilitates the insertion of the shaft into the hub in such away that the slanted wall of the phase presses continuously theexcessive material of the shaft more deeply into the shaft. That area ofthe margin of the hub, where said blunt angle is present, acts howeveras an edge on the shaft. The pressure built up by the compression of theshaft material due to the slanted wall of the phase, grows sudden in theregion of said hub edge. As a consequence, material from the shaftsurfaces may be torn off by said edge. On the joining surface of theshaft or of the hub resp. which are damaged in this way, the fit of thehub on the shaft is not sufficiently well defined.

It is an object of the present invention is to remove said disadvantageas well as further disadvantages of the prior art.

This object is solved by a device of the afore mentioned type inaccordance with the present invention as defined in the characterizingportion of the independent claim 1.

Below, possible embodiments of the present invention are explained inmore detail by means of the enclosed figures. It is shown in:

FIG. 1 a shaft and a hub in a vertical cross-section, before the hub ispressed onto the shaft,

FIG. 2 a hub which is configured as a cam, in a front view

FIG. 3 schematically and in a vertical cut, a detail from a firstembodiment of the present invention,

FIG. 4 schematically and in a vertical cut, a detail from a secondembodiment of the present invention,

FIG. 5 in a lateral view, a detail from a shaft, which comprises axiallyrunning elevations,

FIG. 6 the shaft from FIG. 5 in a cross-section

FIGS. 7 to 11 schematically and in a vertical axial cut, each showing anenlarged detail from a respective, further embodiment of the presentinvention,

FIGS. 12 to 14 details from further embodiments of the hub in a frontview and

FIGS. 15 to 17 a depiction of the manufacture of a hub as shown in FIG.12, in a front-view on the hub

The present device has a shaft 1 and a hub 2 (FIG. 1) which have acommon main axis A. The present device may also comprise several hubs 2on the shaft 1 (not illustrated) In FIG. 1, the hub 2 is spaced in adistance from the shaft 1, i.e. before the hub 2 is placed on the shaft1. This way of illustration of the present device is better suited toclearly show essential features of the present device.

The hub 2 may be worked as a cam disk (FIG. 2) which has been pressedonto the shaft 1. The shaft 1 together with one or several cam disks 2constitutes an assembled camshaft. It is obvious that the hub 2 may alsobe the inside hub of a homo-kinetic joint or a component of a gear,exzenters, a crank-cheek, joint-fork or the like, whereby the hub 2 isbeing joint to the shaft by form locking or frictional contact. Theassembly of shaft 1 and hub 2 may constitute a built crank shaft,mechanism-shaft or driveshaft or a built shaft-fork-connection or thelike.

The hub 2 shown in FIG. 1 has a main body 3, which is essentiallyannular. In this main body 3 an opening 5 is carried out. The wall 6 ofthis opening 5 has the shape of the coat of a geometrical object whosesurface line is a straight line. This geometrical object can be acylinder or a cone, for instance. To the respective one end portion ofthe wall 6 of the opening 5 a margin 10, 30 resp. of the opening 5 isattached. The main body 3 shows further lateral surfaces 7 and 8 whichare positioned essentially perpendicular with respect to the main axisA.

The shaft 1 has essentially cylindrical main body 4. In order that apressure joining between shaft 1 and hub 2 can exist, the shaft 1 showsan excess or overmeasure with respect to the opening 5 in the hub 2.Consequently, the radius r1 of the opening 5 in the hub 2 is smallerthan the radius rw and rp of the shaft 1, respectively, in the contactarea. But it is also possible that the radiuses r1 and rw of the parts 4and 5 of the present device are essentially identical with respect totheir numerical values or that they allow a clearance fit.

FIG. 3 shows schematically and in a vertical cross-section a detail froma first embodiment of the present device. This detail involves only partof the hub 2 and shows one of the margins 10 of the opening 5in the hub2. This margin 10 constitutes a transitional region between the insidewall 6 of the opening 5 in the hub 2 and one of the lateral or frontalareas 7 of the main body 3 of the hub 2. If a vertical cross-section isled in such away that the main axis A of the opening 5 lies in thecross-sectional plane, then the cut across this margin 10 of the opening5 appears as a convex arc 11. That one end section of the curve 11 whichis connecting to the surface line of the wall 6 of the opening 5, lieson the same straight line as the beginning of the said surface line ofthe wall 6.

Otherwise explained, the bent surface 11 of the margin 10 of the opening5 connects itself tangentially to the inner surface 6 of the opening 5.This means that a tangent to the arc 11 forms the surface line of theinner wall of the drill hole at a point of contact T. This point ofcontact T is defined as being common both to the arc 11 and to thesurface line of the inside-wall 6 of the drill hole or opening 5. Thetransition between the arc 11 and the surface line of the opening 5 runscontinuously, i.e. one and only one tangent may run through the point ofcontact T. In the example depicted in FIG. 3; the arc 11 has the shapeof a circular arc with a radius R1. At the point of contact T, betweenthe radius R1 and the surface line of the wall 6 an angle alpha of 90°extends.

At least that one margin 10, which is positioned in the direction of thepressing force, has in longitudinal cross-section an arched shape 11.But it is without all possible, however, that the opposite margin 30 ofthe opening (FIG. 1) also has such a contour line in cross-sectionalview along the longitudinal axis.

The margin 10 of the opening, having the arched profil or longitudinalsection 11, extends between the inner region 6 of the opening 5 in thehub 2 and one of the lateral surfaces 7 or 8, respectively, of the hub2. Thereby, the arc 11 representing the longitudinal cross-sectionthrough the margin 10 may also be tangentially connected to the lateralsurface 7 of the hub 2. This is however not necessary. The angle betawhich extends between the lateral surface 7 of the hub and the terminalportion of the arc 11 connected to said surface 7 may be smaller than180°, as it is apparent from FIG. 3.

FIG. 4 shows schematically and in vertical cross-section a detail from asecond embodiment of the present invention. The margin 15 of the opening5 in this device consists from two arcs 11 and 12, seen in a verticalsection. That one arc 11 of this opening margin 15, which is connectedto the respective surface line of the inner wall 6 of the hub 2 is of aconvex shape. That one arc 12 of the hub interior margin 15, which isgoes over into the lateral surface 7 of the hub, is of a concave shape.The bows 11 and 12 of the profil of the opening margin 15 meet oneanother in such a manner that they go tangentially one another. In theembodiment illustrated here, the bows 11 and 12 are circular arcs havingthe radius R1 and R11. The radius R11 of the second arc 12 is smallerthan the radius R1 of the first arc 11.

That one terminal section of the first arc 11, which is connected to thebeginning of the surface line of the inside wall 6 of the hub opening 5,lies on the same straight line as the beginning of said surface line ofthe inner wall 6. This corresponds to that one situation which isillustrated in FIG. 3, so that also in the case of the embodimentaccording to FIG. 4 a continuous transition without damaging edges isguaranteed. That one terminal section of the second arc 12, whichterminates on the lateral surface 7 of the hub, defines a relativelysteep angle beta with respect to this lateral surface 7 because of theconcave shape of the arc 12.

At such embodiments of the present device, the main body 4 of the shaft1 may have a smooth, cylindrical outer surface 9. But in certainapplications of this device it is necessary that the shaft 1 has anouter surface 9 provided with projections.

FIGS. 5 and 6 show one of such embodiments of the present device wherebythe shaft 1 has said projections. These projections are configured asaxially running elevations 16 which rise from the cylindrical outersurface 9 of the shaft 1. Such elevations 16 can be formed e.g. byembossing or, preferably, by rolling or milling of the material of theshaft 1, or by chip removing techniques. These elevations 16 can beplaced at least in that one area of the length of the shaft 1 which isoccupied by the hub 2 pressed onto the shaft 1.

The vertex or top 18 of the respective elevation 16 is located in adistance s over the outer surface 9 of the shaft 1. The distance of thevertex 18 of the respective elevation 16 from the longitudinal axis Aamounts to N. N equals rw plus s. A shaft configured in this way isassigned to the hub 2 (FIG. 7), the margin 15 of which consists of thearcs 11 and 12. This profile is illustrated in FIG. 4. The distance N isbigger than the radius r1 of the opening 5 in the hub 2.

In order to further increase the stability of the fit of the hub 2 onthe shaft 1, a further embodiment of the present device is foreseen.This embodiment is depicted in FIG. 8 and it is based on the embodimentof the present device described in the foregoing in connection with theFIGS. 5 to 7. The device according to FIG. 8 has circumferentialdeepenings 17 in the inner wall 6 of the opening 5 of the hub 2. Theseessentially annular deepenings 17 are spaced apart from each other andare arranged rectangular with respect to the longitudinal axis A of theopening 5. The depth of the deepenings 17 is at least as big as theheight s of the axially running elevations 16 on the shaft 1. The axialrunning elevations 16 are preferably more rub-resistant or harder thanthe hub 2 in the region of the opening 5.

In the embodiments of this device described in the foregoing, theopening 5 of the hub 2 may be continuously narrower in the widthstarting from the bowed margin 10 and 15, so that the wall 6 of theopening 5 may adopt the shape of a cone. But the magnitude of the radiusr1 of the opening 5 may as well decrease stepwisely. Suchshaft-hub-assemblies offer in high-precision-connections the advantagethat the contact pressure per unit area may be chosen over the entirewidth of the hub 2 in such a manner that the hub 2 after the joining hasparaxial outer surface lines. This measure allows for example to usegrinded tooth-wheels or cams prior to said joining which do not requirefurther grinding or other processing after joining as assembled shafts.

FIGS. 1 and 2 as well as FIG. 9 show another embodiment of the presentdevice. FIG. 9 shows an enlarged detail from this device. Also with thisembodiment, the inside wall 6 of the opening 5 is essentiallycylindrical and the cylinder has the radius r1. In such an opening 5 ofthe hub an axially running bulge or indentation 20 having a depth t ispresent. The wall 21 of this indentation 20 preferably constitutes asection of the a coat of a cylinder, the radius r2 of which is smallerthan the radius r1 of the opening 5 in the hub. The axis B of thissecond cylinder 20 is spaced in a distance e from the longitudinal axisA of the opening 5 in the hub. The axis B runs in parallel to thelongitudinal axis A. The distance e between the axis A and B may bedenoted as excentricity. It is also possible that the wall 21 of theindentation 20 deviates from the exact geometrical cylindrical shape.

The hub 2 illustrated in FIGS. 1 and 2 is carried out as a cam disk. Acam 14 is elevating over the peripheral area 13 of the main body 3 ofthe hub 2. Among other things because of the rigidity it is ofadvantage, to locate the indentation 20 in the hub 2 in such a mannerthat it lies underneath of the cam 14 of the cam disk 2. Thereby it isparticularly of advantage when the indentation 20 is arrangedsymmetrically with respect to the vertical axis C of the cam 14.

The radius r2 of the cylindrical indentation 20 can be smaller than theradius r1 of the opening 5 in the hub 2. Under this relation between theradiuses r1 and r2, an edge 22 is present at that one place where thewalls 6 and 21 of the cylinders 5 and 20 meet one another. This edge 22may be rounded or sharp-edged. Upon pressing of the shaft 1 into theopening 5 in the hub 2, the material of the shaft 1 penetrates into theindentation 20. Thereby said edges 22 in the interior of the opening 5in the hub fit laterally into that material of the shaft 1 which isplaced in the indentation 20. This measure effectively prevents anaccidental free spinning of the shaft 1 in the hub 2 upon high loadingof the shaft assembly.

Between the corresponding end portions of the bulge or of theindentation 20 and the transitional arc 11 an arc 25 extends which istangential connected to the transitional arc 11 and which is alsotangential connected to the surface line of the bulge wall 21 (FIG. 9).This embodiment guarantees a favorable flow of the material during theprocess of joining.

In connection with this embodiment of the hub 2, it can be of advantage,to provide the shaft 1 with circumferential material elevations 26 (FIG.9). These elevations 26 can be the turns of a thread or they may berings or collars on the shaft 1 which are arranged perpendicular withrespect to the longitudinal axis A of the shaft 1. The height of thevertexes 27 of the turns or of the rings 26 over the shaft main body 4can also be denoted as s. The distance between two neighbouringcircumferential elevations 26 can be designated with p (FIG. 1) and thisdistance p may be equal to the width of an elevation 26. The radius rpof the elevations 26 may be equal to the distance M between thelongitudinal axis A of the opening 5 in the hub 2 and that one bottomline 23 in the wall 21 of the indentation 20, which is most distant fromthe longitudinal axis A. The radius rp may also be slightly bigger thanthe distance M.

In principle it is possible to use the shaft 1 with axially runningelevations 16 as illustrated in FIGS. 5 to 8 in connection with a hub 2according to the FIGS. 1 and 2, respectively. The shaft 1 with thecircumferential elevations 26 (FIG. 9) may also be used in connectionwith the other embodiments of the hub 2 disclosed herein.

That one embodiments of the present device having an indentation 20(FIG. 2) can be manufactured starting from a blank of the hub 2 in whichis already provided with a roughly carried out opening 5. In a firststep, the hub opening 5 together with the bent section 11 are exactlymanufactured. Thereby the workpiece, i.e. the blank of the hub 2, standsstill. The manufacturing tool (not illustrated in the figure) is movableand it encompasses a pole-like holder and a projection made up from avery hard material which protrudes from the lateral surface of theholder. Such a boring tool moves along a screw line, the longitudinalaxis of which coincides with the longitudinal axis A and the radius ofwhich is roughly equal to the radius r1. The projection or elevationalways protrudes radially from the pole-like bearer. During this step ofthe method according to the present invention, the sections 6 and 10 or15 of the opening 5 of the hub 2 can be manufactured.

After this first manufacturing step a second boring of the opening 5 inthe hub 2 begins. At the beginning of this second manufacturing step theboring tool is moved along the distance e from the longitudinal axis Aof the hub 2, i.e. towards the wall 6 of the opening 5. Thereafter thetool moves along a screw line, the longitudinal axis of which runs inparallel to the main axis A and the radius of which corresponds to theradius r2. During this manufacturing step the wall 21 of the bulge orindentation 20, the arc 25 and the edges 22 are manufactured.

According to this method the opening 5 of the hub 2, the indentation 20and the arcs 11, 12 and 25 can consequently be manufactured on the samemachine.

If the requirements with respect to the stability of the hub 2 and thedensity of the hub material are not extraordinarily high, in many casesa sintering process is suitable for the manufacturing of the parts ofthe hub 2. In this method, steel powder is squeezed to a so-calledsemifinished piece, which is hardened in a sintering oven to thenecessary hardness. This method is economically most efficient uponmanufacturing large numbers of these pieces. The hub bores having theradiuses r1 and r2 and the corresponding, tangentially running radiusesR1, R11 and R2 can be manufactured according to this method withoutchip-removing treatment.

FIG. 10 shows a still further embodiment of the present device. Theshaft 1 is already equipped with the afore mentioned axial runningelevations. In the inside wall 6 of the hub 2 the circumferentialdeepenings 17 are also carried out as described before. The depth f ofthe deepenings 17 in the hub 2 is at least as big as the height s of theaxially running elevations 16. The axially running elevation 16 ispreferably made from a harder or more rub-resistant material than thehub.

According to the embodiment illustrated in FIG. 11, the hub 2 is fixedon one of the ends of the shaft 1. The end portion of the shaft 1 whichis bearing the hub 2 is equipped with a flange 31 to stop the hub 2. Theradius rw of the shaft 1 and the radius rp of the elevations on theshaft 1, respectively, can be manufactured together with the flange 31by chip-removing techniques, in the case of the present embodiment ofthe invention.

The length of the bulged section 32 of the shaft 1 is chosen in such amanner that a portion 33 of the shaft section 32 sticks out from the hubopening 5. After the hub 2 has been pressed in the above describedmanner onto the shaft 1 up to the stop at the flange 31, the part 33protruding from the opening 5 is additionally formed as to wedge the hub2. The circular flange 34 of the so deformed part 33 resembles aheadpiece of the shaft 1 flattened by hammering, which guarantees anespecially tight fit of the hub 2 on the shaft 1.

FIG. 12 shows an embodiment of the present device, whereby the opening 5in the hub 2 shows a similar contour 5 as the opening 5 of the hub 2according to FIG. 2. The difference between the contours of the openings5 shown in FIGS. 2 and 12 consists in the course of the contour line inthe transition region 24 between the wall 6 of the hub opening 5 and thewall 21 of the indentation 20. In the embodiment illustrated in FIG. 12,the transition region has the shape of an arc 24. This arc 24 can be asection of a circle 28 having a radius r4. This section 24 of a circleis connected tangentially both to the wall 6 of the hub opening and alsoto the wall 21 of the indentation 20. With a hub according to FIG. 2,the contour line of that transition region 24 has an unsteady course sothat an edge 22 is present here on the hub 2.

The shape according to FIG. 12 is manufactured in such a way that a socalled end milling cutter having the radius r2 is introduced in thedrill hole constituting the opening 5 and that this milling cutter ismoved in the opening 5 in such a manner that the arched transitionregion 24 is formed.

The profile of the wall 6 of the opening 5 in the hub according to FIG.13 is a modification of the profile illustrated in FIG. 12. The profileof the wall of the indentation according to FIG. 12 is a compositeprofile which comprises two arcs 211 and 212 and one linear section 213extending between these arcs 211 and 212. The arcs 211 and 212 have anangle length of practically only 90°. One end of each of these arcs 211and 212 is connected tangential to the neighbouring and afore mentionedarched shaped transition region 24. The respective opposite end of therespective arched shaped transition region 24 goes over tangentiallyinto the straight line shaped section 213 of the profile of theindentation 20.

FIG. 14 shows an embodiment of the indentation 20 having an angular, inthe shown case a quadrangular profil.

FIG. 17 shows a further developed embodiment of the profile or of thecontour of the opening 5 in the hub 2, respectively, which are describedin connection with FIG. 12. The hub 2 according to FIG. 17 has fourindentations 20 whereby always two, pairwisely, are diametrally setapart. The contour or profile of the transition region 24 between therespective neighbouring indentations 20 is arc shaped. This arc 24 canbe a section of an circle 28, whereby the end parts of the contour lineof the neighbouring indentations 20 goes over tangentially into the endparts of the respective circular arc 24. Consequently the contour of thewall 6 of the opening 5 in the hub 2 is a curve composed from arcswhereby a convex and a concave arc are alternating. Therefore, thecontour line of this hub opening 5 has the shape of a wave or sinusoidalline.

What is claimed is:
 1. A device having a shaft (1) and at least one hub(2) which is securable on this shaft, said shaft and said hub eachhaving a longitudinal axis (A) and the longitudinal axis of said shaftis coaxial with the longitudinal axis of said hub when said hub issecured to said shaft, wherein: said hub is provided with an interiorwall (6) delimiting an opening (5) that extends along the longitudinalaxis of said hub, and said hub has two lateral surfaces that are spacedapart along the longitudinal axis of said hub; said opening has twomargins (10, 30) each located adjacent a respective one of said lateralsurfaces, and a main part that extends between said margins; at leastone of said margins of said opening has a curved profile (11) in planescontaining the longitudinal axis of said hub; said curved profile meetssaid main part of said opening tangentially; and said opening has afirst radius (r1) and has an indentation (20) in said interior wall, andsaid indentation has the form of a section of a cylinder that has asecond radius (r2) that is smaller than the first radius (r1) and thathas an axis (B) that is offset from the longitudinal axis of said hub bya distance (e).
 2. The device according to claim 1, wherein: saidinterior wall delimiting said opening is configured as a surface of ageometrical structure defined by a generatrix that is a step line or astraight line that is parallel to or convergent with respect to thelongitudinal axis of said hub.
 3. The device according to claim 1,wherein the axis (B) of said cylinder is parallel to the longitudinalaxis of said hub.
 4. The device according to claim 1, said interior walldelimiting said opening meets said indentation (20) at a transitionregion (24) that has an unsteady course so that at least one edge (22)is present along said opening.
 5. The device according to claim 1,wherein: said interior wall delimiting said opening meets saidindentation at a transition region (24) that has a shape of an arc of acircle (28) having a third radius (r4); the third radius is smaller thanthe first radius; and said transition region is convexly oriented suchthat a first end portion of said transition region is connectedtangentially to said interior wall delimiting said opening and a secondend portion of said transition region is connected tangentially to thesaid indentation.
 6. The device according to claim 1, wherein saidindentation has a composite profile composed of two arcs (211,212) andone linear section (213) extending between said arcs (211,212), each ofsaid arcs (211,212) has an angular extent of substantially only 90degrees, one end portion of each of said arcs (211 or 212) is connectedtangentially to an adjacent arch shaped transition region (24) andanother end portion of each of said arcs (211 or 2120 that is oppositeto the one end portion is connected tangentially to said linear section(213).
 7. The device according to claim 1, wherein: said shaft has anouter surface that has a radius and from which project axially (16) orcircumferentially (26) running elevations; each of said elevations has atop that is spaced from the longitudinal axis of said shaft by adistance (N,rp) that is greater than the radius of said outer surface ofsaid shaft; the first radius of said opening in said hub (2) is smallerthan the distance (N,rp) of said elevations the longitudinal axis ofsaid shaft; and said elevations are placed at least in an area of saidshaft that extends through said hub when said hub is secured on saidshaft.
 8. The device according to claim 7, wherein: said elevations onsaid shaft run circumferentially; said elevations are turns of a threador ring or collars on said shaft; said indentation has a portion that ismost distant from the longitudinal axis (A) of said shaft; the distancebetween the top of said elevations and the longitudinal axis of saidshaft is substantially equal to or greater than the distance (M) betweenthe longitudinal axis of said hub and the portion of said indentationthat is most distant from the longitudinal axis of said shaft.
 9. Thedevice according to claim 7, wherein: said elevations on said shaft runaxially; said interior wall of said hub is further provided withcircumferential, substantially annular deepenings (17) that extend in adirection that is substantially perpendicular to the longitudinal axisof said hub; said deepenings are spaced apart from one another along thelongitudinal axis of said hub; each of said deepenings has a depth,perpendicular to the longitudinal axis of said hub, that is at least asgreat as the distance between the tops of said elevations and the outersurface of said shaft; and said elevations are made of a material thatis harder than the material of said interior wall of said hub.
 10. Thedevice according to claim 1, wherein: said curved profile at said one ofsaid margins of said opening is convex; said indentation has an end atsaid one of said margins of said opening, and a main part that extendsfrom said end; said end of said indentation has a section profile (25)that has a convex shape in planes containing the longitudinal axis ofsaid hub; and said second profile extends between said curved profile atsaid one of said margins of said opening and said main part of saidindentation and meets said main part of said indentation tangentially.11. The device according to claim 1, wherein: said curved profile atsaid one of said margins of said opening includes at least first andsecond curved profile sections (11, 12); said first section (11) isconvex and extends from said main part of said opening of said hub; saidsecond section (12) is concave and extends from said first section tothat one of said lateral walls that is adjacent said one of saidmargins; and said first and second sections meet one anothertangentially.
 12. The device according to claim 1, wherein: said shafthas an end portion to which said hub is secured; said end portion ofsaid shaft has a flange or a seat (31) for engaging one of said lateralsurfaces of said hub, a hub supporting section and an end section thatprojects beyond said hub when said hub is secured to hub supportingsection and said one of said lateral faces is bearing against saidflange or seat; and said end section of said end portion is arranged tobe deformed to form a second flange that bears against the other one ofsaid lateral surfaces after said hub has been placed on said hubsupporting section.
 13. The device according to claim 1 wherein, priorto assembly of said shaft with said hub, said shaft has across-sectional shape different from that of said opening in said hub.14. A method for manufacturing the device according to claim 1,comprising: providing a hub blank having a prepared preliminary opening;performing a first boring operation to form the opening (5) that extendsalong the longitudinal axis of the hub and the curved profile (11); andthen performing a second boring operation to form the indentation (20).15. A method for manufacturing the device according to claim 1,comprising carrying out a sintering process to produce the hub (20). 16.A device having a shaft (1) and at least one hub (2) which is securableon this shaft, said shaft and said hub each having a longitudinal axis(A) and the longitudinal axis of said shaft is coaxial with thelongitudinal axis of said hub when said hub is secured to said shaft,wherein: said hub is provided with an interior wall (6) delimiting anopening (5) that extends along the longitudinal axis of said hub, andsaid hub has two lateral surfaces that are spaced apart along thelongitudinal axis of said hub; said opening has two margins (10, 30)each located adjacent a respective one of said lateral surfaces, and amain part that extends between said margins; at least one of saidmargins of said opening has a curved profile (11) in planes containingthe longitudinal axis of said hub; said curved profile meets said mainpart of said opening tangentially; and said interior wall delimitingsaid opening has a contour composed of a plurality convex arcsalternating about the longitudinal axis of said hub with a plurality ofconcave arcs, so that said contour has the shape of a wave line.
 17. Thedevice according to claim 16, wherein: the contour of said interior walldelimiting said opening is composed of four concave arcs formingindentations and four convex arcs forming transition regions; saidindentations are arranged in pairs so that the indentations of each pairare diametrically opposed to one another; and said convex arcs are arcsof circles that meet adjacent concave arcs tangentially.
 18. The deviceaccording to claim 16 wherein, prior to assembly of said shaft with saidhub, said shaft has a cross-sectional shape different from that of saidopening in said hub.